A storage fabric may include multiple storage controllers, including physical and/or virtual storage controllers, which store and manage data on behalf of clients. Applications utilizing such storage systems rely on continuous data availability. Accordingly, with respect to physical storage controllers, one common technique to provide high availability is to cross wire storage drives or fabric between two physical storage controllers to provide a seamless transfer if one of the physical storage controllers fails.
While both physical storage controllers can operate simultaneously, neither physical storage controller should operate at greater than half capacity since each of the physical storage controller may need to service the traffic previously serviced by a failed one of the physical storage controllers. Accordingly, providing high availability in the context of physical storage controllers requires maintaining significantly underutilized storage controllers with excess headroom, which is undesirable particularly considering the relatively high cost of the hardware required to implement the physical storage controllers. Additionally, the pairing of storage controllers is not an optimal solution in platforms requiring significant scalability.
While virtual storage controllers generally require relatively lower cost to implement than physical storage controllers, and therefore underutilization is not a significant concern, platforms on which virtual storage controllers are implemented may not allow sharing of the same storage drives or fabric between virtual storage controllers or, more specifically, the virtual machines on which the virtual storage controllers are executed. Accordingly, cloud platform providers do not offer virtual storage controllers a shared storage fabric.
Instead, high availability for cloud platforms is often implemented using mirroring of the stored data, requiring replication and associated storage costs, which can be significant. Another technique is simply to reboot a failed virtual storage controller. However, rebooting generally takes on the order of several minutes within which applications relying on the services provided by a failed virtual storage controller will generally fail themselves. Therefore, providing high availability of virtual storage controllers on a cloud platform generally results in significant additional storage cost or application disruption and/or failure.